The Form of Combative Strategy in Interactions among Wolf Pups (Canis lupus)

Z. Tierpsychol., 68, 177-200 (1985) @ 1985 Verlag Paul Parey, Berlin und Hamburs ISSN 0044-3573 / Intercode: ZETIAG

Department of Psychology, Dalhousie University, Halifax

The Form of Combative Strategy in Interactions among Wolf Pups ( Canis Zapus)

By ZVIKA HAVKIN and JOHN C. FENTRESS

With 9 figures

Received: June 15,1983

Accepted: July 20, 1984

Abstract and Summary

This study concerns the form of combative interactions between wolf pups and how this form relates to strategy. Filmed records were analysed for dyadic interactions among threc pups between the ages of two weeks and five months. By isolating and recombining the variables of body pitch, snout contact plnccment, and mutual orientation, combative strategies leading to unbalancing (falling) of one partner were evaluated. It was found that consistent dyadic configurations, bite locations and patterns of leg sweeps could be related to three distinct styles of falling (side, back and forward falls). Forward falls developed last, and represent a controlled strategy of active defense. “Top” and “bottom” pups can switch roles but show position-dependent regularities in behavior. These biomechanically defined regularities clarify some problems aswciated with the constructs of play and dominance-submission.

Traditionally, ethologists sought to distinguish between “play” and “serious” fighting (ALDIS 1975) on a number of grounds (LOIZOS 1966, 1967). We examine social combat (“playfighting”) in wolf pups from a mechanical perspective so as to document a series of complex strategies, evident already a t a young age. In doing so our approach complements the traditional by showing formal affinities between the “playful” activity of pups and the “serious7’ combat of adults.

Playfighting in wolf pups involves frequent body contact between the interactants. During such interactions one animal may lose its balance and fall to the ground while its partner (or partners) remains stable. Since we

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178 ZVIKA HAVKIN and JOHN C. FENTRESS

consider loss of balance to be a critical determinant of the form of combative interactions, we examined in detail those interactions in which one of two interacting pups fell to the ground.

At any moment during a dyadic interaction a distinction can be made between the participants, based on their adoption of physically stable roles (stability will be defined later, as a function of the support base). We also identify two different attack modes, each of which may involve the use of the feet, as well as three different styles of falling following loss of balance. We show, then, that “playfighting” (HENRY and HERRERO 1974) or “play- wrestling” (ALDIS 1975; BEKOFF 1974) may be viewed as consisting of a number of combative techniques not less advanced than adult fighting.

When two adult wolves can be consistently distinguished as being either dominant or submissive toward one another, mechanical analysis points to consistent differences in their respective combative strategies. Thus the “dominant” animal is consistently offensive, whereas the “submissive” animal remains defensive. A developmental study of combative techniques in juveniles, then, clarifies some of the controversy related to the concepts of dominance- subordination in caiiid social behavior (LORENZ 1952; SCHENKEL 1967).

Our mechanical viewpoint is based on a “real time” approach to analysis (GOLANI 1976). Although we analyze the behavior in detail, all the regularities we speak of may be observed in the field by any observer.

Data Collection Methods

This report is based on film records of interactions among three wolf pups (Canis lrlpus), filmed between the ages of three weeks and five months.

Subjects: Three wolf pups (Canis lupus) (Nicole, Tatiana: females; Asad: male) were removed from their natal dens at the captive wolf compound in Shubenacadie, Nova Scotia, during May 1979, between 11 and 19 days of age. (For a detailed description of the parental pack, see MORAN and FENTRESS 1979). The pups were housed indoors, and kept under a dark-light cycle of 8-16 h. They received human company for at least 4 h a day. Initially, the pups were fed Borden’s Esbilac, and solid food was introduced a t three weeks of age. Bottle feedings were terminated at the age of 7 weeks.

T h e outdoor pen: At about 6 weeks of age the pups were moved to an outdoor pen, composed of two enclosures, one with a floor area of 221112, the other of 6.5me. The smaller enciosure contained a kennel capable of sheltering all pups together, a large round water pail, and a food dish. The pups were confined to the small pen only during cleaning.

Materials and procedures: All interactions were filmed with a Bolex 16-mm reflex cink camera, a t a rate of 16 frames per s (fps). Film stock consisted of 121-m rolls of Eastman 4X B/W film and Eastman VNF high speed color film.

We started filming the pups indoors when they were three weeks old but only one sequence from that period was used in the analysis. All other sequences were shot after the pups were moved to the outdoor pen. These sessions were carried out either between 06.00 and 08.00 h, or between 17.00 and 19.00 h.

Filming sessions lasted from 10 to 60 min. A session was terminated either when we shot 30-60m of film or after 1 h. The pups were filmed every other day for the first three months. The camera was started whenever any two pups began interacting with (e.g. con- tacting) each other, and stopped when they separated. In the last 6 weeks of filming the above procedure was repeated every fourth day instead of every second day. Before and

The Form of Combative Stratcg) i n Interactions among Wolf Pups 179

during each filming session we took cxtensi\e written notes, so that we could reconstruct the continuity between film takes. Film anal!\is was carried out with an LW photo optical data analyzer.

Besides the filming of the wolf pups described here, we filmed and observed one pair of pups i n 1976 and another pair in 1978. The extensive film record of these pups ( two females in 1976 and a male and a iciiiale in 1978) was used to verify all the results reported later in this study.

Additional obseuv~tioms:

Analytic Techniques and Results

Loss of balance during fighting (playful or serious) is a major factor with respect to continuation of the interaction. In order to examine the process of unbalancing, i.e., what leads to the fall of an animal and how it is executed, we extracted a number of measures from the films.

I. The Analysis Variables First Variable: Body Pitch

Body pitch described the relationship of a pup’s trunk to the ground. This relationship is a function of particular body parts making contact with the ground, and of the degree of extension of the limbs. The pitch is described as one of 6 levels: Level 5 - Standing, with all four legs extended. Level 4 - Sitting on the hind part of the body, with hind legs folded under

and forelegs extended, or crouching on forelegs, hind legs extended. Level 3 - Lying with all four legs folded and the ventral side of the body

touching the ground. Level 2 - Lying on either left or right flank. Level 1 - Lying on the back, all legs in the air. Level O - Unidentifiable body position, always a relatively fast transition

To observe the change in pitch over time, we initially analyzed 8 dyadic and triadic interactions (16000 frames at 16 fps). When data from these analyses were plotted (HAVKIN 1981), a number of sudden drops in pitch from level 5 to level 2 were observed. These drops constitute the main data base described in the text.

A complete fall is a change in body pitch from level 5 to level 2 or 1 occurring within less than 3 s (48 frames). In other words, during a fall a pup’s position changes from standing to lying on one side or on the back. We did not analyze falls initiated when one pup was at level 4 (sitting) since we wanted to be reasonably confident that neither pup had an a priori handicap in the form of reduced stability.

between two levels.

Second Variable: Snout Contact

Since physical contact may influence the interactants’ balance critically, we analysed snout contacts directed by one pup to another. The body surface of a wolf was partitioned into 9 cephalo-caudal zones (cf. OWENS 1975b),

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F i g . 1: An illustration of the outlines of the nine contact zones used for scoring snout contacts. The snout of the pup on the right is oriented toward the head (zone 2) of the pup on the left, so that if contact were established, the score for the pup on the right would be 2. All line drawings of wolf pups were traced from original films by H. H A V K I N

such that the snout was considered as zone 1, the head as 2, etc., and the tip of the tail was scored as 9. When a pup’s snout was neither in contact with, nor oriented toward its partner, contact was scored as 0. The outlines of the 9 zones are shown in Fig. 1, which also illustrates that the zones are numbered in direct relationship to their distance from the snout.

The contact score of an animal is a number between 1 and 9, denoting the zone in which the pup’s snout contacts the partner (i.e., X’s score denotes a zone on Y, in contact with X’s snout).

Third Variable: Mutual Orientation

Mutual orientation describes the angle between the horizontal projections of the pups’ longitudinal axes (regardless of body pitch). The longitudinal axis of each pup was obtained by drawing an imaginary line from the hips to the shoulders, by visual approximation. Only when the spine was fully curved (such as when a dog tries to catch its tail) did we draw the longitudinal axis as a curve. This curve was considered as beginning at the tip of the nose and extending to the tail.

Mutual orientation was scored by drawing the longitudinal axes of the pups as arrows oriented toward each other with an angular resolution of 45’ (an orientation thus scored as 90° means that the angle between the pups could be anywhere from 67S0 to 112.5O). In addition to the angular relation between the pups, the location of each pup’s head relative to the other pup’s body axis was maintained in the arrow drawings. For example, if pup X’s snout was oriented toward pup Y’s shoulders, both the angle between the longitudinal axes of the interactants, and the location of the snout vis-a-vis the shoulders were retained in the drawing. In cases where a pup’s contact score was greater than 0 (see above), the origin of the arrowhead, but not its angular orientation, was a direct function of this variable. Mutual orientation as defined here is a combination of the “relative orientation” and the “opposi-

The Form of Combative Strategy in Interactions among Wolf Pups 181

tion” Eshkol-Wachmann movement notation measures used by GOLANI (1976) and by MORAN et al. (1981), with the exception that we scored only “opposi- tion” of snout to body.

11. The Analysis of Falls We scored only dyadic interactions involving a fall. An interaction was

considered dyadic when two and only two pups were in physical contact just before and shortly after the fall. Only interactions during which no obstacles were present in the pups’ paths were analyzed. The decision to select only dyadic interactions was made to simplify analysis. Also, in almost all triads the third pup joined the interaction after the fall had occurred, so that i t could not influence the fall itself. In the following text the falling pup will be called the “bottom pup” and its partner will be called the “top pup”, but these names should not be taken to imply any other differences between the animals.

Scoring was done frame by frame: body pitch and snout contacts were scored separately for each pup and mutual orientation was scored for both at the same time. A change was noted only when it exceeded the relevant degree of resolution. For example, a deviation of less than 22.5’ on either side of the mutual orientation line was ignored. A change in snout contact was noted only when the contact point moved to a new zone, etc.

We analysed a total of 62 dyadic interactions containing falls, with at least 15 frames recorded on film before and after the fall. Wherever possible, we analysed at least 75 frames before, and 75 frames after the fall. Elsewhere we analysed the available film.

Graphic and Verbal Descriptions of Interactions

In order to illustrate the time courses of the 62 falls they were recon- structed graphically. Three examples were given in Figs. 2 A-C.

Fig. 2 A depicts an interaction filmed when the pups were 32 days old. Both pups were standing. A approached N’s right side and bit her in the middle of the torso, while pushing forward. N lost balance and started falling, so that after 7 frames (less than 0.5 s) the whole left side of her torso hit the floor at once: she was now lying at body pitch level 2. She continued turning until she was lying on her back (level I). Meanwhile, A remained standing (level 5) but shifted his bite to the posterior end of N’s torso (snout contact score6). The mutual orientation changed from 90° to 45’ and N bit A by extending her neck toward him. Later she turned to lie on her side again (level 2) while A crouched on his hind legs and then sat down on all four legs (levels 4 and then 3). At the same time, the angle between them became less obtuse until they were antiparallel (see “Mutual Orientation”). In this configuration they could bite each other on the rump, and as N shifted to level 3, their body pitch became equal.

During the interaction illustrated in Fig. 2 B the pups were 49 days old. They were standing in an antiparallel, head-on mutual orientation. Geo- metrically, this is a symmetric configuration, and indeed, each pup was con-


tacting the other in the neck region (see snout contact plot). T pushed forward, toward A's rear. H e sat (level 4), but remained stable for almost a s. T, however, moved into a rightangel asymmetric position from which she continued to push A while maintaining snout contact with his neck. At this point A lost his balance (see the abrupt change in pitch) and fell to level 2 . The first part of A's body to touch the ground, other than his legs, was his left hip, and the

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line of contact with the ground proceeded along his left side. T dropped slowly until their body pitch became equal.

This interaction illustrates a style of falling different from the one illustrated in Fig. 2 A. Instead of hitting the ground “at once” with the whole side, contact during the fall proceeded from the posterior part of the body to the head. In both cases, nevertheless, the top pup was able to maintain snout contact continuously during the fall of the bottom pup.

In the next interaction, shown in Fig. 2C , the pups were 58 days old. A few s before the fall A was a t T’s side biting her neck. T oriented her snout toward A’s neck but did not secure a grip on his neck. She then oriented her snout between A’s forelegs, lowered her head until it touched the ground, fully extended her hind legs and “rolled” over her head. She fell .with her head touching the ground first, the line of contact with the ground proceeding along her shoulders, back, and side in a cephalo-caudal direction. After this fall had been initiated, A let go of T’s neck, as can be seen in his snout contact plot.

The analysis presented so far will be supplemented by additional analyses and by line drawings, since Figs. 2 A-C and the other similar figures plotted from the scores provide only a simplified spatial representation of the interactions. We will now describe regularities apparent in the behavior of the interacting pups.

111. The “T” Configuration

Of all classes of mutual orientation one occurred at a very high rate during the interactions.

The “T” configuration is an orientation of 90’ ( *22.5O7 see “Mutual Orientation”) between the longitudinal axes of two pups, except when they are a t a snout to snout contact. The snout to snout contact position is excluded because it is a symmetric configuration which appeared in the films for very short periods of time (10 or fewer frames), usually when the pups were changing their mutual orientation.

The Prevalence of the “T” Configuration

Of a total of 6251 frames during which the pups were scored in uncurled positions, they formed a “T” in 2736 frames. These values give an observed probability of 0.438. Consider that this configuration can be established on either the right side or the left side of the pup at the crossbar of the “T”. Also consider that there are 8 rotational positions around the longitudinal axis of an animal. It follows that the geometric probability of the “T” relative to all other configurations is 0.25 (2/8). The observed value shows that the “T” configuration occurred more frequently than would be expected by geometric considerations alone. Inspection of the data shows that this probability pattern was exhibited by all pairs of pups.

The Predictability of the End Position

When a fall occurred while the pups were in a “T”, the outcome followed a highly predictable pattern. In 28 out of 31 such falls the pup at the crossbar

The Form of Combative Strateg) in Interactions among Wolf Pups 185

of the “T” lost balance and fell. Only in about 10 (3 of 31) of the cases did the pup at the crossbar become top pup. This indicates that a position at the stem of the “T” is relatively stable, regardless of which individual occupies that position.

The Mechanics of Unbalancing in the “T” Position

A body is unbalanced when its center of gravity is moved outside of its base of support (LONDEREE 1969; HAY 1973). The force needed to unbalance an object in a certain direction is proportional to the distance of the center of gravity from the point of support in that direction (LONDEREE 1969). In a configuration such as the “T”, a pup at the stem pushing toward the crossbar has a fairly short distance through which to act. In order to unbalance its partner, a pup a t the crossbar, however, must push against a more stable partner. The animal at the stem of the “T”, then, is in a more stable position.

A pup at the crossbar attempting to unbalance its partner by a side push is handicapped by, at least, two factors. First, it is less stable than its partner, and second, it cannot move as efficiently as the other animal (since, for a cursorial canid, a forward movement seems to be anatomically easier to execute). Another handicap at the crossbar is that the wolf at the stem is within easy snout reach of the whole near side of its partner, whereas the animal at the crossbar has a more limited reach. The easy accessibility of the “crossbar” may impart to the pup at the stem a measure of partner-control not available to the other wolf (see also GOLANI 1976).

Iv. The Attack

HENRY and HERRERO (1974) and Fox (1969) state that teeth are the only weapons employed by Canidae in agonistic behavior. Although later we will demonstrate an exception to this rule, there is no doubt that the canines are the sole decisive weapon of most canids. The same weapon, then, must be used both in “offense” and in “defense”. By showing the distribution of bites in various phases of interactions, we were able to show that a distinction between these strategies does exist in wolves.

First, we examined bites immediately preceding falls and delivered by the pup about to become “top pup” (henceforth called “biting attacks”). These were not distributed evenly along the nine contact areas, as can be seen in Fig. 3, which shows the frequency distribution of biting attacks (N = 57) to various zones (see Fig. 1). Since contact zones were numbered as a function of their distance from the snout, the histogram illustrates frequency of attack against distance from the snout.

The overall distribution is bimodal: Zone 5, a large area constituting the anterior half of the torso, received only one attack. One large part of the body, then, received a very small portion of all bites, whereas other parts (e.g. the neck) received a disproportionately large share. The same “biting profile” appeared in each of the pup pairs.

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The bimodal distribution of biting attacks establishes a natural division between two types of attack: An unteriov uttuck is directed to the area between the snout and shoulders

A posterior uttuck is directed to the area between the rear torso and the tip inclusive (contact zones 1-4);

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The Form of Combative Strategy in Interactions among Wolf Pupa 187

After looking at biting attacks we examined all snout contacts delivered b! both the bottom and the top pups, Fig. 4 shows the distributions of these contacts. It illustrates two differences between the snout contact distributions of the two pups. (The units on the ordinate are of relative frequencies.) The first difference is that the bottom pup directed a very high percentage (76.4 70, N 212) of all snout contacts to the anterior part of its partner (zones 1 to 4) but only a few (18.4 %) were directed to posterior zones (6 to 9). In contrast, the top pup directed fewer snout contacts to the anterior zones (53.9%, N = 191) and more contacts to the posterior zones (37.2 ”/.). The second difference is between the contact patterns of the two pups within the anterior area. The top pup directed more contacts to its partner’s neck than to its partner’s head. The bottom pup directed as many or more contacts to its partner’s head as to the neck.

(These differential patterns existed for each of the three pups as a function of its position as top or bottom pup. The phenomenon appears to be e5pecially robust in view of the fact that the pups differed greatly in their overall rate of participation in interactions as a top or a bottom pup. For example, T was top pup in 33 falls and bottom pup in 14, whereas A was top pup in 15 instances and bottom pup in 28. Despite this, both showed the differential snout contact patterns discussed above.)

Top and Bottom Positions as “Offensive” and “Defensive” Roles

The differential biting patterns encountered in our wolves (in rhesus monkeys, SYMONS 1978) seem to be rehted to HENRY and HERRERO’S (1974) single weapon theory. An “offensive” animal using its jaws as an only weapon is likely to reach for a vulnerable body part. Such a part might be the neck (IXYHAUSEN 1979) or the posterior part of the body, since i t is far from the head, therefore hard to defend (see the discussion in GOLANI 1976). The “defense” against such a bite, on the other hand, could be either to stop the approaching jaws, or to deflect them. I n either case, a defensive animal would direct its weapon toward the head of the attacker. An animal on the offensive, then, would distribute its snout contact? relatively evenly between anterior and posterior zones, whereas a defensive animal would concentrate more of its snout contacts at the anterior parts of its partner.

The two divergent patterns are correlated with the position of “top” or “bottom” animal in any one interaction. This fact suggests that the biting pattern is not related to the position of an animal in a social hierarchy. Rather, it is a consistent strategy, a role, that each pup may assume for a certain portion of the interaction as a function of its physical positioning within an interacting dyad. Thus, a pup such as T, who became top pup twice as often as bottom pup, still exhibited the expected defensive mode when she happened to be in the bottom position.

Fig. 2 D illustrates an extreme case of a differential biting pattern, where the bottom pup, A, establishes contact only with the head, neck and snout of hi$ partner, T. She, on the other hand, contacts A only in the hips and posterior torqo.


V. The Fall

The way an animal falls during vigorous physical activity is of major biological import (HAY 1973, p. 96). Theoretically, continuation of the activity might be impossible if the body sustains a high impact during a fall. In the case of agonistic behavior, the time it takes an animal to recover from impact might determine its likelihood of survival. Moreover, a good falling technique can be used to advantage in some circumstances (e.g. in Judo: KUDO 1966).

To find out how wolf pups fall, we looked at all interactions involving a fall, with regard to the first body parts to touch the ground. All falls were thus classified into one of three types: Class 1. A whole side of the animal touched the ground a t once. For example,

the left hip, left side of torso, and left shoulder came into contact with the ground within two frames (0.125 s).

Class 2. The first body part to touch the ground was one hip. Thereafter contact progressed in a caudo-cephalic direction.

Class 3. The first body parts to touch the ground were one side of the head, and/or one side of the neck, and/or one shoulder. Thereafter contact progressed in a cephalo-caudal direction.

As a result of our analysis we were able to show a developmental gradient in the different classes of falling. The existence of this gradient, and some biomechanical properties of these classes of falls illustrate, in the following section, that falling techniques can be incorporated in the overall defensive strategy of the individual.

VI. The Side Fall

Side falls (class I ) were seen in an interactive context a t three weeks of age. At this age the pups were so poorly coordinated that they would frequently fall without any apparent external cause. We decided, therefore, to start analyzing falls only when the pups seemed to be relatively stable on their feet, a t about one month of age. Fig. 2 A shows an interaction involving a side fall and Fig. 5 illustrates such a fall as a series of line drawing traced from a film. It highlights the distinctive feature of the fall, namely, that one side of the bottom pup hit the ground almost at once, and as the body hit the ground there was no horizontal vector to the movement. At the instant of impact, then, almost all the momentum generated during the fall was vertical and i t was absorbed within 1/8 s.

The Mechanics of Unbalancing in the Side Fall

All side falls in which the mutual orientation could be determined (N=9) were preceded by a “T” configuration, with the bottom pup always a t the crossbar. All side falls were also preceded by a biting attack accompanied by a movement of the top pup’s forefoot directed toward either the fore or hind legs of the bottom pup. Specifically, the attack leading to a side fall always consisted of a bite and a “leg sweep”. The concurrent action of a bite


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Fig . 5 : A series of drawings illustrating ,z side fall preceded by a foreleg sweep. The corresponding frame numbers are under the drawings, 16 fpb

and a leg sweep forms a couple (a couple consists of two parallel and equal forces acting in opposite directions - see HAY 1973, p. 108; TRICKER and TRICKER 1967, p.167). With one “hooked” forepaw the top pup pulled the fore or hind legs from under the bottom pup, while pushing with its snout in the other direction. The result of this complex manceuvre, when successful, was that one of the bottom pup’s bases of support was removed, while its body was pushed in the direction of the removed base. This type of movement is used in wrestling as a way of minimizing the effort needed to unbalance and topple an opponent (BORING 1975, p. 270). It is also the principle behind most leg techniques in Judo (KUDO 1966, p. 127; WALKER 1980).

The leg sweep is illustrated in Fig. 5. The left foreleg of the top pup swept both forelegs of the bottom pup. The interaction proceeded so quickly that the camera lags behind the pups and the line drawings do not show all the details. As we continued to follow the interaction we saw that the bottom pup hit the ground flat on its side, within the three frames following frame 12. In other falls the bottom pup’s hind legs, instead of its forelegs, were swept (Fig. 6 in HAVKIN 1981).

Mechanically, the leg sweep can be applied optimally from the stem of a “T”. From a parallel configuration the snout push would be directed against a distant, and therefore stable, base of support (the hind legs). In contrast, the side fall appeared fast and direct when initiated from a “T” position. The bottom pup could not easily regain its balance by a lateral step, since one of its bases of support was pulled in the other direction. Although an attempt might have been made to regain balance by shifting one of the unswept feet, it was not very likely to succeed. During our observations of the films, and


as the pups grew older, we noticed that consistent and usually successful attempts were made to avoid leg sweeps by the partner. Indeed, it appeared that wolf pups can use their legs as weapons. Although they need not cause injury directly, the limbs can be used strategically to manipulate the partner into a position from which biting i t might be easier.

VII. The Back Fall

Class 2 falls were named “back falls”. The first back fall was seen in an interactive context when the pups were 40 days old. Back falls start with lowering of the hind quarters (the bottom pup drops to sitting), the torso becomes unbalanced to one side and contact is gradually established between the torso and the ground in a caudo-cephalic direction (see the description in the text of Fig. 2B). In almost all cases the unbalancing was biased toward one side, such that the characteristic line of contact with the ground advanced along one of the sides of the torso (i.e. along the ribs and not along the neural spines of the vertebrae).

Back falls were preceded either by anterior attacks (N=13) or by posterior attacks (N = 15). Figs. 6 and 7 illustrate back falls initiated by a posterior attack (Fig. 6 ) and by an anterior attack (Fig. 7). The figures demonstrate an important structural aspect of this type of fall. The trunk of the pup rolled

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F i g . 6 ; A back fall preceded by a posterior attack

The Form of Combative Strategj in Interactions miong Wolf Pups 191

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to rest relatively slowly in such a way that as each successive section of the body came into contact with the ground it was already supported by parts closer to the tail.

The Time Course of the Bark Fall

The durations of all back falls were measured by counting the number of frames from the beginning to the end of each fall. The beginning was defined as the frame in which the first body part other than the legs (section v) touched the ground. The end of a fall was defined as the frame after which no additional parts of the trunk came into contact with the ground. The mean duration of back falls preceded by an anterior attack was 13.4 frames (S.D. =

10.44) or 0.84 s‘). Back falls preceded by a posterior attack had a mean duration of 9.9 frames (S.D. = 4.06) or 0.63 s. Back falls took longer to complete thm did side falls which, by definition, lasted no more than two frames. Com- pared to the side fall, kinetic energy is lost more gradually, in the back fall, fulfilling one of the requirements of safc falling (COOPER and GLASSOW 1973, p. 261; WELLS 1966, p. 137).

1) Note : Standard deviations calculated here are based on scores combined for different animals; they are intended to provide the reader with a summary of our actual population of observations, and are no^ to be used as a basi\ for any other form of sta- ti.;tical inference.


The Mechanics of Unbalancing in the Back Fall

1. Posterior Attack Reactions to posterior attacks were more uniform than reactions to

anterior attacks, in that posterior attacks were followed by back falls in 15 out of 17 cases. Anterior attacks were followed by any one of the three classes of falls.

The reaction to posterior attacks consisted of an inside turn in the horizontal plane while orienting toward the top pup’s anterior (Fig. 6). In an inside turn a pup orients toward the side from which the attack came. Wolves have been observed to respond to a posterior contact by a human (a tail pull to one side) by an inside turn (FENTRESS 1967) and we have seen this response on numerous occasions with dogs.

Turning toward the head of the top pup, while the bottom pup’s rear end was held stationary by the partner’s bite, caused the bottom pup’s spine to curl. The curling (or incurvation) brought the bottom pup’s hips to the ground, a sequence of events similar to a dog chasing its tail and lowering its hind quarters while doing it. In such a curled position complete unbalancing is a matter of a slight push (for a detailed discussion see HAVKIN 198 1, Appendix A).

2. Anterior Attack

The turn

When attacked from the front a pup responded in one of three ways: first was to turn its head up and toward the top pup, the second was to its head laterally away from the attack, and the third was to turn its

head and/or its shoulders down, toward the ground. The first and second ways of reacting always led to a back fall (N 1 13), and the third way resulted in a class 3 fall. Here we discuss only attacks that ended in a back fall (class 2).

The lateral movement away from the attack, as well as the upward turning of the head, unbalanced the bottom pup toward its rear end. This perhaps caused the fall to start from the hips. The unbalancing of the bottom pup, then, was helped either by a lateral shift of the center of gravity, close to the edge of the base of support, or by an upward shift of the center of gravity, which also resulted in reduced stability.

VIII. The Forward Fall

The forward fall (class 3) is illustrated in Figs. 2 C and 8. In this fall one side of the head-neck-shoulder region comes into contact with the ground first and contact proceeds cephalo-caudally thereafter. Similarly to back falls, forwards falls were usually “biased” to one side such that the line of contact from the head to the posterior of the torso proceeded along the ribs, not the neural spines. The hind legs usually left the ground, and the whole trunk of the pup “flipped” over its head. The sequence of movements in the forward fall resembles the forward roll in a number of martial arts (HISATAKA 1976, p. 132; KUDO 1966, p. 42; So 1970, p. 51; YAMADA 1969, p. 20).

The Form of Combative Srraregy in Interactions among Wolf Pups 193

78 80 82 66 70 74

94 96 98 101 103 Fig . 8: A forward fall. Note the legwork in frame 78: with his left foreleg the top pup (Asad) “hooks” the left foreleg of the bottom pup (Tatiana), while stepping on her left

hind leg with his right foreleg

During interactions leading to forward falls the attacking pup frequently secured a grip on the neck or shoulders of the defending pup, and sometimes attempted a leg sweep, as illustrated in Fig. 8, frame 78 and later 84-92.

The first interaction containing a forward fall was filmed when the pups were 5 3 days old. However, motor activity akin to the forward fall was seen earlier on three occasions. Once they started executing the fall it was seen as frequently as the other falls. After day 5 3 we found 14 more forward falls, 8 back falls preceded by an anterior attack, and 11 more back falls preceded by a posterior attack.

The Time Course of the Forward Fall

The mean duration of forward falls was 9.9 frames * S. D. 3.86 (0.62 s, N=15). This mean duration is very close to that of a back fall originating in a posterior attack. It is shorter than a back fall initiated from an anterior attack, but its variability is less.

The forward fall fulfills the requirements for safe falling, that kinetic energy be lost gradually (WELLS 1966), and that vertical momentum be trans-

%. Tierpsydiol., Bd. 68, Heft 3 14


ferred to horizontal momentum upon contact with the ground (COOPER and GLASSOW 1973).

Unbalancing in the Forward Fall

Forward falls were accompanied by two consecutive postural changes in the bottom pup. First, the shoulders were lowered, thereby dropping the center of gravity and increasing the stability of the bottom pup (LONDEREE 1969). The second change was harder to assess, but i t was observed in a t least the first 10 forward falls. It consisted of full extension of the hind legs, as can be seen in Fig. 8 (compare frames 94 and 96). This extension elevated the bottom pup’s hips and decreased its stability. Although it was not possible to evaluate the relative physical contributions of each of the two pups to the fall, research on the sport of Judo provides data relevant to this question.

In a kinetic analysis of basic Judo techniques, IKAI and MATSUMOTO (1958) showed that when a technique is applied, the center of gravity of the defense (the player about to be thrown) is higher than the center of gravity of the offense. Consequently, the defense in Judo training is advised to lower its center of gravity as much as possible to avoid being thrown (KUDO 1966). Lowering the center of gravity increases the stability of the Judo player, and forces the offense to invest more energy in the throwing attempt. The relationship between the centers of gravity applies in all techniques except in leg sweeps which employ a “couple” action (section VI).

The studies of IKAr and MATSUMOTO (1958) and LONDEREE (1969) suggest that if the bottom pup were to lower its shoulders without the subsequent elevation of the hips, the fall might have been delayed or prevented. Since the elevation of the hips did not appear to be caused by any physical con- comitants of the bottom pup’s posture, we hypothesized that the bottom pup might have been “assisting” in projecting itself over its head and shoulders.

In the next section we will examine this conjecture, and show how the bottom pup’s behavior can be viewed as an active (and adaptive) defensive strategy.

The Back Fall Compared to the Forward Fall

During or immediately following all forward falls, the top pup released contact with the bitten target on the bottom pup’s anterior. In contrast, in only 5 of 13 back falls was contact with the bottom pup’s anterior released. The high rate of contact release during forward falls could be explained by two factors. The first was that because of the form of the forward fall it was always accompanied by a very pronounced neck rotation perpendicular to the neck‘s longitudinal axis (see Fig. 8). Since all pups were approximately equal in size, the rotation was bound to have exerted a considerable torque on the top pup’s jaws, and brought about a release of contact.

In addition to the torque on the neck, the structure of the forward fall implies a major change in orientation caused by the bottom pup. Fig. 9 illustrates that two changes of 180’ occurred in the middle of the interaction. The


Fig. 9: Digits 1-5 at the tail of the straight line vectors indicate the

bottom pup (Tatiana). Digits on the arcs tha t connect these position

changes (in framea, 16 fps)

sequential position changes of the 2

changes indicate the duration of the 3

4 5

TAT1 A N A t

A CAMERA

first such change took about 11 frames to complete and it was accomplished by a slow lateral shift of T's hind legs. The second change was carried out very quickly, in about two frames, and it was done by a forward fall. Similarly, in other forward falls substantial changes in the bottom pup's orientation were achieved in a very short time. In comparison, orientation \hifts during back falls were of less than 90" and they took more time to complete.

Another distinguishing aspect of the two types of falls was their time course. As noted earlier (sections VII and VIII) back falls preceded by anterior attacks had a mean duration of 0.84 s, whereas forward falls had a mean duration of 0.62 s. These observations agree with the hypothesis that the time course of forward falls is more predictable than that of back falls.

The form of the forward fall illustrates another mechanically significant quality. In the back fall the position of the hips on the ground was kept constant, and the rest of the body trailed behind. In the forward fall the oppo- \ite was true - the position of the head was kept constant and the rest of the body trailed behind. In the back fall, then, the trajectory and final position of the head could not be fully determined in advance by the bottom pup. In the forward fall, however, the position of the head was set before the fall by the bottom pup. Since the head carries most of the bottom pup's weaponry, the ability to control its final position can be an advantage. The forward fall was preceded by a seemingly active elevation of the hips that broke the top

14::.


pup’s hold, suggesting that the bottom pup projected itself without being forced to do so. While the predictability of the final head position and of the duration of the forward fall permitted the top pup to calculate the end position of the bottom pup’s head and to plan to be there, we have instead shown that during the forward fall the top pup was forced to break contact more often than during a back fall. In addition, in both types of falls the top pup could follow the head visually and at a short distance. In such circumstances, the predictability of both the final location of the head and of the duration of the fall could have benefited only the bottom pup, suggesting that the forward fall is used as an active defense.

Discussion

In our work we have regarded as a strategy a series of movements consistent with the achievement of a physically advantageous end position. Though we have not found in the literature similar systematic descriptions of the combative strategies of other species, many descriptions of animal combat, predation and play illustrate the use of combative forms discussed here. These examples show that the forms we studied (the “T” configuration, the patterns of biting, the styles of falling) can be viewed largely as generalized forms of combat with inter-specific variations (see HAVKIN 1981 for a more detailed review).

As brief examples one may mention that the “T” configuration is strategically important in fights between the male Hercules beetles (Dynastes hercules; BEEBE 1944, 1947), in male-male aggression of many ungulates (WALTHER 1974), etc. The observed advantages of a position at the stem of the “T” are similar in many diverse species, hinting at analogous mechanical factors.

Similarly, offensive vs. defensive biting patterns have been described in rhesus monkeys (SYMONS 1978), where they resemble those described by us in wolf pups. These patterns indicate that the same pattern may exist in many species that employ the teeth as the main weapon system.

Lastly, the forward fall, commonly termed “rolling over”, has been illustrated in cats (LEYHAUSEN 1979, p. 187: during adult fighting), in arctic foxes (Fox 1971, p. 68: during play), in bears (HENRY and HERRERO 1974); in Viverridae (HINTON and DUNN 1967) and in other species. Our results indicate that this form appears in “playful” contexts without evidence of exaggeration when compared to its shape when seen in a “serious” context.

Conclusions

We have demonstrated that the combative patterns outlined here are inter-related such that the resulting nexus might be called strategies for obtaining a mechanical advantage over one’s partner. The reader may now


ask how the adoption of such strategies is related to general ethological questions. We will discuss briefly two issues upon which, we believe, the present study sheds light.

1. The Definition of Dominance-Submission in Canid Social Behavior

Most observers of wolf social behavior agree that consistent asymmetric relationships persist between wolves of the same sex and the same pack (SCHENKEL 1967; MECH 1970). These social asymmetries are commonly named “dominance-submission” relations, although such terminology is often unclear (cf. LOCKWOOD 1979). It is usually claimed that the animal with erect ears and tail, a high frequency of urination etc., is the “superior” (SCHENKEL 1967; but see LORENZ 1952) or “supplanting” (MORAN et al. 1981) animal. O n the other hand there is considerable evidence that the animal so classified as superior is frequently found a t the crossbar of the “T” (same authors).

We have already discussed the mechanical disadvantages at the crossbar. Our view, that it is a mechanically inferior position to the stem, is consistent with SCHENKEL’S view that when a superior wolf is found at the crossbar, its apparent disadvantage presents a challenge to the inferior.

It is impossible to know what a challenge means to a wolf. Our approach implies that the regularities observed in the “dominance-submission” relationship stem from a systematic difference in the combative strategies of the two interactants. Whereas the superior wolf employs an entirely offensive strategy, the submissive wolf is defensive. Thus, when the superior lunges at the inferior’s rear, the inferior may turn inside (section VII, posterior attack), getting its rump away from the attack and facing its opponent, yet not attacking though it is at the stem of a <‘”’.

2. The Practice Hypothesis of Play

Many authors suggest that animals practice aggressive skills during play (ALDIS 1975; FAGEN 1981; HINTON and DUNN 1967; OWENS 1975a and b). Some claim that play reveals an “evolutionary design”, specifically adaptive for the practice of such skills ( G ~ o o s 1901; SYMONS 1978). In order to support this last claim SYMONS argues that some characteristics postulated as specific to play are part of the “evolutionary design” (his term), that is, they help the interactants become better fighters in a shorter period of time. These postulated characteristics include the supposed exaggeration of movements, and the supposed inhibition of biting.

We found no evidence that combative activity of wolf pups is either exaggerated or uneconomical, nor did we find any evidence that the pups inhibit their biting. In fact, we showed that during play wolf pups exhibit aspects of behavioral sophistication not demonstrably exceeded at later developmental phases. In this respect our results are consistent with previous studies that failed to show exaggeration of movement in play (HENRY and HERRERO 1974; HILL and BEKOFF 1977). We believe that the concept of play-

198 ZVIKA HAVKIN and JOHN C. FENYRESS

fighting has not been properly distinguished from any other kind of fighting in young wolves (hence we use the term "combative social behavior").

Zusammenfassung

Untersucht wurden die aggressiven Handlungen von jungen Wolfen und ihre Kampfstrategie. Die Analyse basiert auf Filmaufnahmen von 2 Wochen bis 5 Monate alten Wolfsjungen. Naher analysiert wurden Interaktionen von Zweiergruppen (dyadic interactions), sofern hierbei eines der Jungen zu Fall gekommen war. Registriert wurden drei Variable: 1. der Vevtikalanteil der Korperposition jedes Jungen (body level), 2. die Position der Schnauze auf dem Korper des Gegenibers (snout contact), 3 . der Hovizontalanteil der Kor- perposition jedes Jungen in bezug auf seinen Partner (mutual orientation). Aus 62 Interaktionen wird jeweils beschrieben: I. die Position der Beteiligten vor dem Fall, 2. auf welche Weise eines der beiden Jungen aus dem Gleich- gewicht kam, 3 . die Reaktion des aus dem Gleichgewicht gekommenen Jungen.

Nach der Bildung einer T-ahnlichen Stellung blieb in 90% aller Falle dasjenige Junge stehen (top pup), das die Basis des T bildete, wahrend das andere Junge zu Boden fie1 (bottom pup). Das ,,top pup" und das ,,bottom pup" zeigten zudem unterschiedliches Beiflverhalten. Mit Hilfe dieser Ver- haltensweisen wurden Angriff und Verteidigung definiert. Es gibt drei ver- schiedene Formen des Fallens, je nachdem, welche(r) Korperteil(e) zuerst den Boden beruhrt. Nach der Mechanik des Vorganges zu urteilen ist das Fallen, das mit dem Korpervorderteil beginnt, die am weitesten entwickelte schutzende Falltechnik. Sie trat als letzte wahrend der Entwicklung auf.

Es wurde der Versuch gemacht, biomechanische Grundlagen des beobach- teten Verhaltens zu beschreiben, weil wir glauben, dai3 fur jede Kampfsitua- tion zunachst die mechanischen Anforderungen untersucht werden sollten, bevor z. B. soziale Zwange als Grund fiir ein bestimmtes Verhalten postuliert werden.

Es werden keinerlei Annahmen uber ,,Ernst" oder ,,Vergniigen" bei die- sem Verhalten gemacht, doch sind die Ergebnisse von Bedeutung fur Unter- suchungen von Kampf und Spiel. Die Ergebnisse werden in bezug auf die Hypothese diskutiert, daf3 Spiel sich als Obung fur adulte Aggression entwickelte.

Acknowledgements

The research for this paper was carried out by the first author 3s part of the requirements for the Ph. D. degree at Dalhousie University. He wishes to thank the Killam Trust, the School of Graduate Studies at Dalhousie University and the George S. Wise Post Doctoral Fellowship Fund at Tel Aviv University for financial support. He also wishes to thank H. HAVKIN for the h e drawings and Dr. P. NAU, N. BENNETT, Dr. I. GOLANI, Dr. J. MATES and Dr. E. HALEVI for their extensive technical help. Research expenses were defrayed in part by NSERC and MRC grants to the second author. We thank Ms. C . J. RYON for maintaining our main pack. Dr. A. FROHLICH generously provided the German summary.


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200 HAVKIN and FENTRESS, The Form of Combative Strategy

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Authors’ addresses: Zvika HAVKIN, Applied Data Research, Route 206 and Orchard Road, CN-8 Princeton, New Jersey 08540, U.S.A.; John C. FENTRESS Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J1.

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The Form of Combative Strategy in Interactions among Wolf Pups (Canis lupus)